Date: Fri, 04 Nov 2005 15:07:21 -0700 From: Scott Long <scottl@samsco.org> To: user <user@dhp.com> Cc: freebsd-fs@freebsd.org Subject: Re: UFS2 snapshots on large filesystems Message-ID: <436BDB99.5060907@samsco.org> In-Reply-To: <Pine.LNX.4.21.0511041531210.8180-100000@shell.dhp.com> References: <Pine.LNX.4.21.0511041531210.8180-100000@shell.dhp.com>
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user wrote: > Hello, > > Considering a PC server running FreeBSD with 4 400 GB hard drives attached > to a hardware raid controller doing raid-5. > > So this will present itself to the OS as a 1.2TB filesystem. > > Any comments on taking one or multiple snapshots of a filesystem of this > size ? > > Given current disk capacities, I would not exactly consider this 1.2TB > filesystem a "large" one ... any comments on say ... a 6-8 TB filesystem > and making one or more snapshots of it ? > > Assume they are marginally busy - perhaps a 5-10% data turnover per day... > > Thanks. > The UFS snapshot code was written at a time when disks were typically around 4-9GB in size, not 400GB in size =-) Unfortunately, the amount of time it takes to do the initial snapshot bookkeeping scales linearly with the size of the drive, and many people have reported that it takes considerable amount of time (anywhere from several minutes to several dozen minutes) on large drives/arrays like you describe. So, you should test and plan accordingly if you are interested in using them. Scott
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